1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile machine, or a multifunction peripheral integrating copier, printer, and facsimile machine, and an image forming method.
2. Description of the Related Art
Conventionally, because of the development of environmental consciousness as seen in a movement for protection of forests as paper resources, printing on a non-printed surface of a paper, double sided printing, and printing on a recycled paper, have been popular so as to reduce the number of papers used for the image forming apparatus such as a copier, a printer, a facsimile machine, or a multifunction peripheral integrating the copier, printer, and facsimile machine.
Furthermore, there are known methods of recycling papers, i.e., a method of separating toner on the paper mechanically or chemically therefrom and a method of using toner which is color fadable as applying heat, light, or chemical (for example, U.S. Pat. No. 5,605,777 and Jpn. Pat. Appln. KOKAI Publication No. 5-191607).
Among the above-described methods of reducing the number of papers used for printing, the latter method of separating toner on the paper or using the toner which is color fadable has more effective paper saving effects than those of the former method of printing on the non-printed surface of the paper or double sided printing.
The above-described method of separating toner on the paper damages the paper by peeling the toner out from the paper, thereby lowering the durability of toner after printing on that paper, and furthermore, this method is not efficient because the toner has to be peeled from every page. Also, the method of using a chemical has a problem in a process of treating the chemical.
The method of using the toner which is color fadable is more effective than the method of separating toner on the paper. Although color of the toner can be erased, other components than coloring component remain thereon. For this reason, slight printed markings remain, and repeating the process of printing→erasing→printing→erasing gives numerous layers of markings which darken the surface. Further, in order to secure effective color fading function, image concentration is set to be lower than that when using general non-fadable toner.
Among the above two problems, when copying the paper with printing of the color fadable toner on which the toner was erased once or plural times prior to the printing, the background with the remaining markings is recognized as an “image” and is treated as an image after reading, and the actual printing on the reused paper generally is very light because of the lower concentration thereof, so that the actual printed portion is recognized as a light image print. Then, when the printed paper is copied, the image portion on the paper becomes light and the erased portions on the background of the paper appear on the copied paper, making the copy difficult to be read. Regarding the facsimile, a desired image cannot be transmitted because of the image in the case of copying described above, and in addition, a desired image cannot be obtained even with the scanner.
Especially, to improve these problems with the color fadable toner, operations such as adjusting the background of the paper and concentration, or changing the range corrected intensity when an image forming apparatus has an image process adjustment function.
However, plural steps are necessary to perform the operations, which makes it more complicated and requires to go through these steps every time when using a copying, faxing, or scanning function, thereby significantly decreasing the efficiency. Also, there is no means for obtaining a desirable image by using an image forming apparatus without an image process adjustment function which enables users to perform variable adjustment.